1. Field of the Invention
The present invention relates to a pneumatic tire, and more particularly, to a pneumatic tire which exhibits excellent stability and controllability on wet roads (hereinafter referred to as controllability) or a combination of excellent controllability on wet roads and excellent comfort of ride even when a vehicle is vibrating (hereinafter referred to as ride comfort) throughout the life of the pneumatic tire including the initial, intermediate, and final periods of tire use.
2. Description of the Related Art
In recent years, as the higher power, higher performance, and longer life have been desired of automobiles, tires have been increasingly required to have more excellent controllability or a combination of more excellent controllability and ride comfort than hitherto throughout the life of the pneumatic tire. Particularly for passenger tires, highly excellent controllability or a combination of highly excellent controllability and ride comfort is strongly required as the tire structure changes from a bias structure to a radial structure and the aspect ratio of radial tires changes from 82 to 72 and further to 65.
To satisfy the requirement, various compounding ingredients used in rubber compositions for tire treads have been examined. As for the vulcanization accelerator, it is disclosed in Japanese Patent Application Laid-Open No. 58-87138 that a rubber composition comprising a specific vulcanization accelerator and a specific antioxidant shows improved resistance to hardening under heating and provides a tire showing improved appearance in the final period of tire use. However, performances of the tire during driving are not examined at all. It is disclosed in Japanese Patent Application Laid-Open No. 56-139542 that scorching in mixing to prepare a rubber composition can be improved by the use of a rubber composition comprising a specific vulcanization accelerator. However, performances of a tire are not described or suggested at all. With respect to inorganic fillers, it is disclosed in Japanese Patent Application Laid-Open No. 10-53003 that a rubber composition comprising alumina provides a tire showing improved controllability in the initial period of tire use. However, the improved controllability cannot be maintained in the intermediate to final periods of tire use.